JP7559337B2 - Ethylene-based polymerization catalyst component, method for producing ethylene-based polymerization catalyst, and method for producing ethylene-based polymer - Google Patents

Description

Application of Article 30, Paragraph 2 of the Patent Act On October 17, 2018, in the Abstracts of the 48th Petroleum and Petrochemical Symposium, page 217, a study on "Ethylene polymerization using Phillips catalyst with planar silica aggregate as a carrier" invented by Hirokane Hirotaka and Yamamoto Kazuhiro was published.

Application of Article 30, Paragraph 2 of the Patent Act On October 18, 2018, at the 48th Petroleum and Petrochemical Symposium, Hirokane Hiroto and Yamamoto Kazuhiro announced their research on "Ethylene polymerization using Phillips catalyst with planar silica aggregate as a carrier," which they invented.

The present invention relates to an ethylene-based polymerization catalyst component, a method for producing an ethylene-based polymerization catalyst, and a method for producing an ethylene-based polymer. More specifically, the present invention relates to an ethylene-based polymerization catalyst component capable of producing an ultra-high molecular weight ethylene polymer, a method for producing an ethylene-based polymerization catalyst, and a method for producing an ethylene-based polymer.

Ethylene-based polymers are key materials that represent plastic materials in industrial fields. Ethylene-based polymers are widely used in a wide variety of technical fields, and therefore require a wide range of properties, such as molecular weight distribution and flowability, as well as mechanical and thermal properties, depending on the application and molding method.
In order to produce such ethylene polymers, various polymerization catalysts have been developed and improved. Among them, Phillips catalysts are used in addition to Ziegler catalysts and metallocene catalysts. Phillips catalysts are chromium catalysts in which a chromium compound is supported on an inorganic oxide carrier such as silica, silica-alumina, or silica-titania, and activated in a non-reducing atmosphere to convert at least some of the supported chromium atoms into hexavalent chromium atoms. Phillips catalysts produce ethylene polymers with a wide molecular weight distribution, and generally have good moldability, making them suitable for blow molding and the like.

In large blow-molded products, creep resistance and impact resistance are important properties. When ethylene polymers with a wide molecular weight distribution obtained using conventional Phillips catalysts are blow-molded into large products, the resulting molded products do not necessarily have a sufficient balance between creep resistance and impact resistance. Creep resistance and impact resistance are contradictory physical properties, and generally, when creep resistance improves, impact resistance decreases, and conversely, when impact resistance improves, creep resistance decreases.

Therefore, if an ethylene polymer having both excellent physical properties such as creep resistance and moldability can be obtained using a Phillips catalyst, it will be a material having a better balance of physical properties and moldability than the conventional level. However, since it is difficult at the present stage to precisely control the catalyst using the Phillips catalyst to introduce an appropriate amount of long chain branches of an appropriate length in an appropriate molecular weight region, no specific guidelines have yet been obtained for a method of improving both physical properties and moldability.
In an attempt to obtain an ethylene polymer having a good balance of physical properties and moldability using a Phillips catalyst, the use of a carrier having a specific structure has been investigated. For example, Patent Document 1 and Patent Document 2 disclose the use of highly porous silica having a specific surface area, average pore volume, and average pore diameter. Patent Document 3 discloses a technique for broadening the molecular weight distribution of a polymer by combining a Phillips catalyst obtained from silica having a specific structure with an organoaluminum compound. Furthermore, Patent Document 4 discloses the use of silica having a unique pore structure and crystallinity.
However, it is difficult to control the molecular weight distribution and composition distribution of the polymer using these catalysts, and it has not been possible to design a catalyst that will produce the desired material properties.

Therefore, attempts have been made to polymerize high molecular weight components and low molecular weight components using separate catalysts. For example, if a high molecular weight component with a high molecular weight and a wide molecular weight distribution is produced, and a low molecular weight component with a low molecular weight and a narrow molecular weight distribution is produced at the same time, the high molecular weight component can be increased and the low molecular weight component can be decreased, and both creep resistance and impact resistance can be improved. From this perspective, Patent Document 5 discloses that high molecular weight polyethylene can be obtained by a Phillips catalyst using a clay mineral as a carrier. Patent Documents 6 and 7 disclose that the molecular weight distribution of the obtained polymer can be controlled by combining a clay mineral with ordinary silica.
As described above, various catalysts have been developed and various ethylene polymers have been synthesized, but the ethylene polymers produced using existing catalysts may not provide the desired effects. Therefore, as one variation of ethylene polymers, an ethylene polymer having an ultra-high molecular weight component is desired.

Special Publication No. 2002-533536 Patent No. 5821746 Special Publication No. 2006-512454 Special Publication No. 2007-517962 JP 2006-257255 A JP 2008-150566 A International Publication No. 2002/088196

The present invention has been made in view of the above-mentioned circumstances, and aims to provide an ethylene-based polymerization catalyst component capable of producing an ethylene-based polymer having an ultra-high molecular weight component. The present invention also aims to provide a method for producing an ethylene-based polymerization catalyst capable of producing an ethylene-based polymer having an ultra-high molecular weight component, and a method for producing an ethylene-based polymer having an ultra-high molecular weight component. In order to solve the above-mentioned problems, the present inventors have conducted extensive research and found that an ethylene-based polymer having an ultra-high molecular weight component can be produced by using an ethylene-based polymerization catalyst component having a specific infrared spectrum and chemical composition, and have completed the present invention based on this finding. The present invention can be realized in the following forms.

[1] An ethylene polymerization catalyst component, comprising an inorganic oxide having the following properties 1 and 2, as measured after calcination at 600° C. for 24 hours as a pretreatment for analysis:
Property 1: In an infrared spectrum, the ratio Py/Px of a peak intensity Py having a maximum in a range Y of 3700 cm ^-1 to 3799 cm ^{-1 to a peak intensity Px having a maximum in a range X of 3600 cm -1 to} 3699 cm ^-1 is less than 10.
Property 2: Contains 90% or more by weight of _SiO2 .

[2] The ethylene-based polymerization catalyst component according to [1], characterized in that the inorganic oxide has a peak at 2θ = 23° to 29° in powder X-ray diffraction that indicates crystallinity with a half-width of 0.2° to 5°.

[3] A step (I) of supporting a chromium compound on the ethylene-based polymerization catalyst component described in [1] or [2] above;
A step (II) of calcining and activating the chromium compound-supported component obtained in the step (I) at 400° C. to 900° C. in a non-reducing atmosphere to convert at least a part of chromium atoms into hexavalent chromium atoms;
2. A method for producing an ethylene polymerization catalyst comprising the steps of:

[4] The method for producing an ethylene-based polymerization catalyst according to [3], characterized in that in step (I), the chromium compound-supported component containing 0.01% by weight to 2.0% by weight of chromium atoms is obtained.

[5] The method for producing an ethylene-based polymerization catalyst according to [3] or [4], characterized in that in step (II), 50% or more of the chromium atoms contained in the chromium compound-supported component are oxidized to hexavalent chromium.

[6] A method for producing an ethylene-based polymer, comprising polymerizing a monomer containing at least ethylene using an ethylene-based polymerization catalyst obtained by the method for producing an ethylene-based polymer according to any one of [3] to [5] above.

By using the ethylene-based polymerization catalyst component of the present invention, it is possible to provide an ethylene-based polymerization catalyst capable of producing an ethylene-based polymer having an ultrahigh molecular weight component.
According to the process for producing an ethylene polymer catalyst of the present invention, it is possible to produce an ethylene polymerization catalyst capable of producing an ethylene polymer having an ultra-high molecular weight component.
According to the process for producing an ethylene polymer of the present invention, an ethylene polymer having an ultra-high molecular weight component can be produced.

1 is a graph showing infrared spectra of Example 1 and Comparative Example 1. FIG. 2 is a schematic diagram for explaining a plate thickness T and D/T of an inorganic oxide particle B1. 1 is a SEM image of chromium catalyst A1.

Hereinafter, the present invention will be described specifically and in detail for each item.
In this specification, when a numerical range is described using "to", the range includes the lower limit and the upper limit unless otherwise specified. For example, the description "10 to 20" includes both the lower limit "10" and the upper limit "20". In other words, "10 to 20" has the same meaning as "10 or more and 20 or less".

1. Ethylene-Based Polymerization Catalyst Component The ethylene-based polymerization catalyst component is characterized by containing an inorganic oxide having the following properties 1 and 2, as measured after calcination at 600° C. for 24 hours as a pretreatment for analysis.
Property 1: In an infrared spectrum, the ratio Py/Px of a peak intensity Py having a maximum in a range Y of 3700 cm ^-1 to 3799 cm ^{-1 to a peak intensity Px having a maximum in a range X of 3600 cm -1 to} 3699 cm ^-1 is less than 10.
Property 2: Contains 90% or more by weight of _SiO2 .

2. Inorganic oxide particles B1 as inorganic oxide
As an inorganic oxide having the properties 1 and 2, the following inorganic oxide particles B1 are preferably exemplified.

(1) Characteristics of inorganic oxide particles B1
Property 1 is that in an infrared spectrum, the ratio Py/Px of a peak intensity Py having ^{a maximum in a range Y of 3700 cm -1 to} 3799 cm ^-1 to a peak intensity Px having a maximum in a range X of 3600 cm ^-1 to 3699 cm -1 is less than 10.
In the infrared spectrum, the peak appearing near 3550 cm ⁻¹ is derived from hydrogen-bonded OH groups. The peak appearing near 3650 cm ⁻¹ is derived from OH groups at sites that cannot interact with others. On the other hand, the peak appearing near 3750 cm ⁻¹ is derived from isolated OH groups on the outer surface. Inorganic oxides that satisfy the requirements of the above-mentioned characteristic 1 have a relatively strong peak intensity near 3650 cm ⁻¹ . This indicates that inorganic oxide particles B1 have a structure that contains many OH groups that are not involved in dehydration condensation even when heated to high temperatures. Such a structure is considered to be a thermally stable regular structure, and it is presumed that the regularity of the structure affects the arrangement of the OH groups.
In the graph of FIG. 1, the infrared spectrum of one example of inorganic oxide particles B1 (Example 1 described below) is shown by a solid line.

(2) Characteristics 2 of Inorganic Oxide Particles B1
Characteristic 2 is a characteristic that the inorganic oxide particles B1 contain 90% by weight or more of _SiO2 . In other words, the inorganic oxide particles B1 are inorganic oxides whose main component is _SiO2 . The content of _SiO2 in the inorganic oxide particles B1 may be 90% by weight or more, but is preferably 95% by weight or more, and more preferably 98% by weight or more. Of course, the content of _SiO2 may be 100% by weight. Since the inorganic oxide particles B1 are particles whose main component is _SiO2 , it is easy to control the shape of the inorganic oxide and has excellent catalytic performance.
When the content is less than 100% by weight, the remaining components may be any inorganic oxide components, but are preferably oxides containing metals of Groups 2, 3, 4, and 13 of the Periodic Table (Periodic Table according to the 1990 Rules for the Nomenclature of Inorganic Compounds).Specific examples include magnesia (MgO), alumina (Al ₂ O ₃ ), titania (TiO ₂ ), zirconia (ZrO ₂ ), and composite oxides thereof, i.e., alumina-titania (Al ₂ O ₃ -TiO ₂ ), alumina-magnesia (Al ₂ O ₃ -MgO), alumina-zirconia (Al ₂ O ₃ -ZrO ₂ ), titania-magnesia (TiO ₂ -MgO), titania-zirconia (TiO ₂ -ZrO ₂ ), etc. Of these, magnesia, alumina and titania are preferred, with alumina and titania being more preferred.

(3) Powder X-ray Diffraction of Inorganic Oxide Particles B1 Inorganic oxide particles B1 preferably have a peak showing crystallinity with a half width of 0.2° to 5° at 2θ = 23° to 29° in powder X-ray diffraction. When inorganic oxide particles B1 are crystalline, the molecular weight of the ethylene-based polymer tends to be increased.

(4) Surface Area of Inorganic Oxide Particles B1 The surface area of inorganic oxide particles B1 is not particularly limited. From the viewpoint of supporting chromium atoms in a dispersed state, the surface area is preferably 10 m ² /g or more and 1000 m ² /g or less, more preferably 20 m ² /g or more and 500 m ² /g or less, and even more preferably 50 m ² /g or more and 400 m ² /g or less.

(5) Pore Volume of Inorganic Oxide Particles B1 The pore volume of the inorganic oxide particles B1 is not particularly limited, but the pore volume is preferably 0.05 to 5 mL/g, and more preferably 0.1 to 3 mL/g.

(6) Shape of the inorganic oxide particles B1 The shape of the inorganic oxide particles B1 is not particularly limited. For example, the inorganic oxide particles B1 may have a plate-like particle shape (first embodiment).
Alternatively, the inorganic oxide particles B1 may contain aggregates of plate-like inorganic oxide particles B1 (second embodiment). In this second embodiment, the inorganic oxide particles B1 may be composed of aggregates only. In addition, in this second embodiment, aggregates of plate-like inorganic oxide particles B1 and non-aggregated plate-like inorganic oxide particles B1 may be mixed.
The plate thickness T (nm) of the plate-like inorganic oxide particles B1 is not particularly limited. From the viewpoint of maintaining the crystalline structure and maintaining dispersibility in the polymer during polymerization, the average plate thickness T (nm) of the inorganic oxide particles B1 is preferably 1 nm or more and 100 nm or less, more preferably 5 nm or more and 50 nm or less, and even more preferably 10 nm or more and 40 nm or less.
The average plate thickness T (nm) of the inorganic oxide particles B1 is determined by measuring the plate thickness T (nm) of 10 inorganic oxide particles B1 with a scanning electron microscope (SEM) and averaging the measured values. Fig. 2 is a schematic diagram of an SEM image of the inorganic oxide particles B1 observed with a scanning electron microscope, and shows the plate thickness T (nm).
The average value of D/T, which is the ratio of the maximum diameter D (nm) of the inorganic oxide particles B1 to the plate thickness T (nm), is not particularly limited. From the viewpoint of being present as a plate-like structure in the particles, the average value of D/T is preferably 10 or more, more preferably 20 or more, and even more preferably 30 or more. The upper limit of the average value of D/T is not particularly limited, but is usually 2000.
The average value of D/T is obtained by observing 10 inorganic oxide particles B1 with a scanning electron microscope (SEM). That is, the average value of D/T is obtained by using 10 inorganic oxide particles B1, calculating D/T, which is the ratio of the maximum particle diameter D (nm) to the plate thickness T (nm) for each particle, and averaging the values. FIG. 2 is a schematic diagram of an SEM image when inorganic oxide particles B1 are observed with a scanning electron microscope, and the maximum diameter D (nm) is shown. The D/T of each particle can be obtained from this maximum diameter D (nm) and the above-mentioned plate thickness T (nm).

3. Inorganic oxide particles B2 as inorganic oxide
The ethylene-based polymerization catalyst component can contain inorganic oxide particles B2 in addition to inorganic oxide particles B1.
The inorganic oxide particles B2 are amorphous.
The inorganic oxide particles B2 are preferably composed of at least one type of particles selected from the group consisting of particles whose main component is silica (SiO ₂ ), particles whose main component is silica-titania (SiO ₂ -TiO ₂ ), and particles whose main component is silica-alumina (SiO ₂ -Al ₂ O ₃ ). Here, the main component refers to a substance whose content (wt %) is 90 wt % or more.
The silica (SiO ₂ ) content in the particles whose main component is silica (SiO ₂ ) may be 90% by weight or more, preferably 95% by weight or more, and more preferably 98% by weight or more. Of course, the silica (SiO ₂ ) content may be 100% by weight.
The total content of silica (SiO ₂ ) and titania (TiO ₂ ) in the particles whose main component is silica-titania (SiO ₂ -TiO ₂ ) may be 90% by weight or more, preferably 95% by weight or more, and more preferably 98% by weight or more. Of course, the total content of silica (SiO ₂ ) and titania (TiO ₂ ) may be 100% by weight.
The total content of silica (SiO ₂ ) and alumina (Al ₂ O ₃ ) in the particles whose main component is silica-alumina (SiO ₂ -Al ₂ O ₃ ) may be 90% by weight or more, preferably 95% by weight or more, and more preferably 98% by weight or more. Of course, the total content of silica (SiO ₂ ) and alumina (Al ₂ O ₃ ) may be 100% by weight.
Among these, from the viewpoints of ease of controlling the particle shape of the inorganic oxide and catalyst performance, it is preferable that the inorganic oxide particles B2 are particles whose main component is silica (SiO ₂ ).
When particles whose main component is silica-titania (SiO ₂ --TiO ₂ ) are used, the particles contain titanium atoms in an amount of 0.2 to 40% by weight, preferably 0.5 to 30% by weight, and more preferably 1 to 20% by weight, as the metal component.
Furthermore, when particles whose main component is silica-zirconia (SiO ₂ --ZrO ₂ ) are used, the particles contain 0.2 to 40% by weight, preferably 0.5 to 30% by weight, and more preferably 1 to 20% by weight, of zirconium atoms as the metal component.
Furthermore, when particles whose main component is silica-alumina (SiO ₂ -Al ₂ O ₃ ) are used, the particles contain 0.2 to 40% by weight, preferably 0.5 to 30% by weight, and more preferably 1 to 20% by weight, of aluminum atoms as the metal component.

The surface area of the inorganic oxide particles B2 is not particularly limited. From the viewpoint of supporting chromium atoms in a dispersed state, the surface area is preferably 100 m ² /g or more and 1000 m ² /g or less, more preferably 150 m ² /g or more and 950 m ² /g or less, and even more preferably 200 m ² /g or more and 900 m ² /g or less.

The pore volume of the inorganic oxide particles B2 is not particularly limited. From the viewpoint that the chromium atoms are supported in a dispersed state and that the particles are easily disintegrated during polymerization to allow the polymer to grow, the pore volume is preferably 0.1 mL/g or more and 5.0 mL/g or less, and more preferably 0.2 mL/g or more and 3.0 mL/g or less.

4. Method for Producing an Ethylene-Based Polymerization Catalyst The method for producing an ethylene-based polymerization catalyst includes the steps of: (I) supporting a chromium compound on an ethylene-based polymerization catalyst component;
A step (II) of calcining and activating the chromium compound-supported component obtained in the step (I) at 400° C. to 900° C. in a non-reducing atmosphere to convert at least a part of the chromium atoms into hexavalent chromium atoms;
Includes.

4.1 Production method of chromium catalyst A1 In the production method of an ethylene-based polymerization catalyst, when the ethylene-based polymerization catalyst component contains inorganic oxide particles B1, the production method is as follows (the ethylene-based polymerization catalyst produced by this production method is referred to as chromium catalyst A1).
The method for producing the chromium catalyst A1 includes the steps of: a step (I) of supporting a chromium compound D on inorganic oxide particles B1; and a step (II) of calcining and activating the inorganic oxide particles B1 supporting the chromium compound D obtained in the step (I) at 400° C. to 900° C. in a non-reducing atmosphere, thereby converting at least a portion of the chromium atoms into hexavalent chromium atoms.

Here, the chromium catalyst A1 will be described. The chromium catalyst A1 is a catalyst in which a chromium compound C1 is supported on inorganic oxide particles B1.
Chromium catalyst A1 is a chromium catalyst in which at least some of the chromium atoms are hexavalent, and is generally classified as a catalyst known as a Phillips catalyst.
An outline of this catalyst is described in the literature such as Kazuo Matsuura and Naotaka Mikami (eds.), "Polyethylene Technology Reader," p. 81, 2001, Kogyo Chosakai, M. P. McDaniel; Advances in Catalysis Vol. 33 p. 47 (1985), Academic Press Inc., M. P. McDaniel "Handbook of Heterogeneous Catalysis," p. 2400 (1997) VCH, M. B. Welch et al. "Handbook of Polyolefins Synthesis and Properties," p. 21 (1993) Marcel Dekker. The chromium catalyst A1 is generally produced by contacting inorganic oxide particles B1 (inorganic oxide support) with a chromium compound D described below and activating the mixture in a non-reducing atmosphere.

The chromium compound C1 is not particularly limited as long as it is a chromium compound in which at least some of the chromium atoms are hexavalent. For example, the chromium compound C1 is derived from chromium oxide, chromium halide, oxyhalide, chromate, dichromate, nitrate, carboxylate, sulfate, chromium-1,3-diketo compound, chromate ester, etc. (hereinafter, the trivalent chromium compounds such as chromium oxide to chromate ester listed here are also referred to as "chromium compound D"). The chromium compound D is supported on the inorganic oxide particles B1 and then activated in a non-reducing atmosphere to become the chromium compound C1. The hexavalent chromium compound C1 may be directly supported on the inorganic oxide particles B1.
More specific examples of the chromium compound D include chromium (III) oxide, chromium trichloride, chromyl chloride, potassium chromate, ammonium chromate, potassium dichromate, chromium nitrate, chromium sulfate, chromium acetate, tris(2-ethylhexanoate)chromium, chromium acetylacetonate, bis(tert-butyl)chromate, etc. In particular, chromium compound D is preferably chromium (III) oxide, chromium acetate, or chromium acetylacetonate.
It is known that even when a chromium compound having an organic group, such as chromium acetate or chromium acetylacetonate, is used, the organic group portion is burned by activation in a non-reducing atmosphere, which will be described later, and ultimately reacts with hydroxyl groups on the surface of the inorganic oxide support, as in the case of using chromium (III) oxide, and at least a part of the chromium atoms becomes hexavalent and is fixed in a chromate ester structure (see V. J. Ruddick et al.; J. Phys. Chem. Vol. 100, p. 11062 (1996); S. M. Augustin et al.; J. Catal. Vol. 161, p. 641 (1996)).

In step (I), the following methods can be used. Suitable examples include a method in which the inorganic oxide particles B1 are impregnated with a chromium compound D solution and then the solvent is removed, and a method in which the chromium compound D is sublimated without using a solvent. Other known methods can also be used. The supporting method is appropriately selected depending on the type of chromium compound D used.
Furthermore, during the production of the inorganic oxide particles B1, a raw material to which the chromium compound D has been added beforehand may be used, thereby directly obtaining the inorganic oxide particles B1 carrying the chromium compound D.

In step (I), inorganic oxide particles B1 may be obtained that support chromium compound D containing 0.01% to 2.0% by weight of chromium atoms. The content of chromium atoms in chromium catalyst A1 is not particularly limited, but from the viewpoint of preventing the supported chromium atoms from agglomerating with each other and being efficiently activated, it is preferably 0.01% to 2.0% by weight, more preferably 0.1% to 2.0% by weight, and even more preferably 0.2% to 1.5% by weight.

In step (II), the inorganic oxide particles B1 carrying the chromium compound D obtained in step (I) are fired in an activation furnace to activate the inorganic oxide particles B1. The activation is carried out in a non-reducing atmosphere that is substantially free of moisture. For example, the activation is carried out in oxygen or air, but an inert gas may also be present. Preferably, the activation is carried out under a fluidized state using air that has been sufficiently dried by passing molecular sieves or the like through the air.
The activation temperature is 400°C to 900°C, preferably 430°C to 900°C, and more preferably 450°C to 850°C. The activation time is not particularly limited. The activation time is preferably 30 minutes to 48 hours, more preferably 1 hour to 35 hours, and even more preferably 2 hours to 30 hours. By the activation, at least a part of the chromium atoms of the chromium compound D supported on the inorganic oxide particles B1 is oxidized to hexavalent atoms, and as described above, the chromium compound C1 is chemically fixed on the inorganic oxide particles B1. If the activation is performed at a temperature lower than 400°C, the polymerization activity decreases, and if the activation is performed at a temperature higher than 900°C, sintering occurs and the activity decreases.

During the supporting or activation of chromium compound D, a known method for adjusting the ethylene polymerization activity or the molecular weight and molecular weight distribution of the resulting ethylene polymer may be used in combination with the addition of a fluorine compound such as ammonium silicofluoride or ammonium hydrogen difluoride, a titanium alkoxide such as titanium tetraisopropoxide, a zirconium alkoxide such as zirconium tetrabutoxide, an aluminum alkoxide such as aluminum tributoxide, an organoaluminum such as trialkylaluminum, an organomagnesium such as dialkylmagnesium, or a metal alkoxide such as an organometallic compound.
In these metal alkoxides or organometallic compounds, the organic group portion is burned by activation in a non-reducing atmosphere, and is oxidized to a metal oxide such as titania, zirconia, alumina or magnesia, which is contained in the catalyst. In addition, the fluorine compound is thermally decomposed during activation to fluorinate the inorganic oxide support.
These methods are generally or in detail described in documents such as C. E. Marsden; Plastics, Rubber and Composites Processing and Applications Vol. 21 p. 193 (1994), T. Pullukat et al.; J. Polym. Sci., Polym. Chem. Ed. Vol. 82 p. 118 (1980), M. P. McDaniel et al.; J. Catal. Vol. 82 p. 118 (1983).

In step (II), it is preferable that 50% or more of the chromium atoms contained in the inorganic oxide particles B1 carrying the chromium compound D are oxidized to a hexavalent state. More preferably, 60% or more of the chromium atoms contained in the inorganic oxide particles B1 carrying the chromium compound D are oxidized to a hexavalent state. The upper limit of the chromium atoms oxidized to a hexavalent state is 100%. The proportion of chromium atoms oxidized to a hexavalent state is adjusted by the activation temperature and time.
The total amount of chromium atoms can be measured by a general metal analysis method, such as plasma emission spectrometry or X-ray fluorescence spectrometry. The valence of chromium can be roughly known by visually observing the color change of the solid product (generally, hexavalent chromium is yellow to orange, trivalent chromium is green, and divalent chromium is blue), but for quantitative analysis, chelate titration and absorptiometry are known as simple methods. Specifically, it is described in "Experimental Chemistry Lecture 15 Analysis" edited by the Chemical Society of Japan, Maruzen (1991), pp. 246-248. For example, in the case of trivalent chromium, an excess of EDTA (ethylenediaminetetraacetic acid) of a known concentration is added to trivalent chromium in an acidic solution, boiled for 5-10 minutes, and titrated with a standard solution of trivalent iron to quantitatively determine the amount. In addition, in the case of hexavalent chromium, it is possible to quantitatively determine the amount by measuring the absorbance at a wavelength of 366 nm, taking advantage of the fact that it exists as CrO ₄ ^2- in an alkaline solution.

4.2 Production method of chromium catalyst A2 In the production method of an ethylene-based polymerization catalyst, when the ethylene-based polymerization catalyst component contains inorganic oxide particles B2, the production method is as follows (the ethylene-based polymerization catalyst produced by this production method is referred to as chromium catalyst A2).
The method for producing the chromium catalyst A2 includes a step (III) of supporting a chromium compound E on inorganic oxide particles B2, and a step (IV) of calcining and activating the inorganic oxide particles B2 supporting the chromium compound E obtained in the step (III) at 400° C. to 900° C. in a non-reducing atmosphere to convert at least a portion of the chromium atoms to a hexavalent form.

Here, the chromium catalyst A2 will be described.
The chromium catalyst A2 is formed by supporting a chromium compound C2 on amorphous inorganic oxide particles B2.
The chromium catalyst A2 is a chromium catalyst in which at least some of the chromium atoms are hexavalent, and is generally classified as a catalyst called a Phillips catalyst.
An outline of this catalyst is described in the literature such as Kazuo Matsuura and Naotaka Mikami (eds.), "Polyethylene Technology Reader," p. 81, 2001, Kogyo Chosakai, M. P. McDaniel; Advances in Catalysis Vol. 33 p. 47 (1985), Academic Press Inc., M. P. McDaniel "Handbook of Heterogeneous Catalysis," p. 2400 (1997) VCH, M. B. Welch et al. "Handbook of Polyolefins Synthesis and Properties," p. 21 (1993) Marcel Dekker. The chromium catalyst A2 is generally produced by contacting amorphous inorganic oxide particles B2 (inorganic oxide support) with a chromium compound E described below and activating the mixture in a non-reducing atmosphere.

The average particle size of the particles of the chromium catalyst A2 is not particularly limited. From the viewpoint of handling, the average particle size is preferably 0.001 μm or more and 200 μm or less, more preferably 0.005 μm or more and 150 μm or less, and even more preferably 0.01 μm or more and 100 μm or less.
The average particle size of the particles of chromium catalyst A2 can be determined by measuring the particle size of 20 particles of chromium catalyst A2 using a scanning electron microscope (SEM) and averaging the measured values. In this study, the average particle size of particles with an average particle size of 0.1 μm or more was determined using a particle size distribution measuring device using the laser diffraction method, and the average particle size of particles with an average particle size of less than 0.1 μm was determined by SEM observation.

The chromium compound C2 is not particularly limited as long as it is a chromium compound in which at least some of the chromium atoms are hexavalent. For example, the chromium compound C2 is derived from chromium oxide, chromium halide, oxyhalide, chromate, dichromate, nitrate, carboxylate, sulfate, chromium-1,3-diketo compound, chromate ester, etc. (hereinafter, the trivalent chromium compounds listed here, such as chromium oxide to chromate ester, are also referred to as "chromium compound E"). The chromium compound E is supported on the inorganic oxide particles B2, and then activated in a non-reducing atmosphere to become the chromium compound C2. The hexavalent chromium compound C2 may be directly supported on the inorganic oxide particles B2.
More specific examples of the chromium compound E include chromium (III) oxide, chromium trichloride, chromyl chloride, potassium chromate, ammonium chromate, potassium dichromate, chromium nitrate, chromium sulfate, chromium acetate, tris(2-ethylhexanoate)chromium, chromium acetylacetonate, bis(t-butyl)chromate, etc. In particular, chromium compound E is preferably chromium (III) oxide, chromium acetate, or chromium acetylacetonate.
It is known that even when a chromium compound having an organic group, such as chromium acetate or chromium acetylacetonate, is used, the organic group portion is burned by activation in a non-reducing atmosphere, which will be described later, and ultimately reacts with hydroxyl groups on the surface of the inorganic oxide support, as in the case of using chromium (III) oxide, and at least a part of the chromium atoms becomes hexavalent and is fixed in a chromate ester structure (see V. J. Ruddick et al.; J. Phys. Chem. Vol. 100, p. 11062 (1996); S. M. Augustin et al.; J. Catal. Vol. 161, p. 641 (1996)).
The chromium compound C1 and the chromium compound C2 may be the same or different.
Moreover, chromium compound D and chromium compound E may be the same or different.

In step (III), the following methods can be used. Suitable examples include a method of impregnating the inorganic oxide particles B2 with a chromium compound E solution and then distilling off the solvent, and a method of sublimating the chromium compound E without using a solvent. Other known methods can also be used. The supporting method is appropriately selected depending on the type of chromium compound E used.
Furthermore, during the production of the inorganic oxide particles B2, a raw material to which the chromium compound E has been added beforehand may be used, thereby directly obtaining the inorganic oxide particles B2 carrying the chromium compound E.

In step (III), inorganic oxide particles B2 may be obtained that support chromium compound E containing 0.01% to 2.0% by weight of chromium atoms. The content of chromium atoms in chromium catalyst A2 is not particularly limited, but from the viewpoint of preventing the supported chromium atoms from agglomerating with each other and being efficiently activated, it is preferably 0.01% to 2.0% by weight, more preferably 0.1% to 2.0% by weight, and even more preferably 0.2% to 1.5% by weight.

In step (IV), the inorganic oxide particles B2 carrying the chromium compound E obtained in step (III) are fired in an activation furnace to activate the inorganic oxide particles B2. The activation is carried out in a non-reducing atmosphere that is substantially free of moisture. For example, the activation is carried out in oxygen or air, but an inert gas may also be present. Preferably, the activation is carried out under a fluidized state using air that has been sufficiently dried by passing through a molecular sieve or the like.
The activation temperature is not particularly limited. The activation temperature is 400°C to 900°C, preferably 430°C to 900°C, and more preferably 450°C to 850°C. The activation time is not particularly limited. The activation time is preferably 30 minutes to 48 hours, more preferably 1 hour to 35 hours, and even more preferably 2 hours to 30 hours. If the activation is performed at a temperature lower than 400°C, the polymerization activity decreases, and the molecular weight distribution of the obtained polymer becomes broad, so that the durability improves but the impact resistance decreases. If the activation is performed at a temperature exceeding 800°C, the molecular weight distribution of the obtained polymer becomes narrow, so that the impact resistance improves but the durability decreases. Furthermore, if the activation is performed at a temperature exceeding 900°C, sintering occurs and the activity decreases. By the activation, at least a part of the chromium atoms of the chromium compound E supported on the inorganic oxide particles B2 is oxidized to hexavalent, and as described above, the chromium compound C2 is chemically fixed on the inorganic oxide particles B2.

During the supporting or activation of the chromium compound E, a known method for adjusting the ethylene polymerization activity or the molecular weight and molecular weight distribution of the obtained ethylene polymer by adding a fluorine compound such as ammonium silicofluoride or ammonium hydrogen difluoride, a titanium alkoxide such as titanium tetraisopropoxide, a zirconium alkoxide such as zirconium tetrabutoxide, an aluminum alkoxide such as aluminum tributoxide, an organoaluminum such as trialkylaluminum, an organomagnesium such as dialkylmagnesium, or a metal alkoxide, or an organometallic compound, may be used in combination.
In these metal alkoxides or organometallic compounds, the organic group portion is burned by activation in a non-reducing atmosphere, and is oxidized to a metal oxide such as titania, zirconia, alumina or magnesia, which is contained in the catalyst. In addition, the fluorine compound is thermally decomposed during activation to fluorinate the inorganic oxide support.
These methods are generally or in detail described in documents such as C. E. Marsden; Plastics, Rubber and Composites Processing and Applications Vol. 21 p. 193 (1994), T. Pullukat et al.; J. Polym. Sci., Polym. Chem. Ed. Vol. 82 p. 118 (1980), M. P. McDaniel et al.; J. Catal. Vol. 82 p. 118 (1983).

In step (IV), it is preferable that 50% or more of the chromium atoms contained in the inorganic oxide particles B2 carrying the chromium compound E are oxidized to hexavalent chromium. More preferably, 60% or more of the chromium atoms contained in the inorganic oxide particles B2 carrying the chromium compound E are oxidized to hexavalent chromium. The upper limit of the chromium atoms oxidized to hexavalent chromium is 100%. The proportion of chromium atoms oxidized to hexavalent chromium is adjusted by the activation temperature and time.
The total amount of chromium atoms can be measured by a general metal analysis method, such as plasma emission spectrometry or X-ray fluorescence spectrometry. The valence of chromium can be roughly known by visually observing the color change of the solid product (generally, hexavalent chromium is yellow to orange, trivalent chromium is green, and divalent chromium is blue), but for quantitative analysis, chelate titration and absorptiometry are known as simple methods. Specifically, it is described in "Experimental Chemistry Lecture 15 Analysis" edited by the Chemical Society of Japan, Maruzen (1991), pp. 246-248. For example, in the case of trivalent chromium, an excess of EDTA (ethylenediaminetetraacetic acid) of a known concentration is added to trivalent chromium in an acidic solution, boiled for 5-10 minutes, and titrated with a standard solution of trivalent iron to quantitatively determine the amount. In addition, in the case of hexavalent chromium, it is possible to quantitatively determine the amount by measuring the absorbance at a wavelength of 366 nm, taking advantage of the fact that it exists as CrO ₄ ^2- in an alkaline solution.

4.3 Production method of chromium catalyst A3 In the production method of an ethylene-based polymerization catalyst, when the ethylene-based polymerization catalyst component contains inorganic oxide particles B1 and inorganic oxide particles B2 (mixed carrier), the production method is as follows (the ethylene-based polymerization catalyst produced by this production method is a mixture of chromium catalyst A1 and chromium catalyst A2, and this is referred to as chromium catalyst A3).
The method for producing the chromium catalyst A3 includes a step (V) of supporting a chromium compound D on inorganic oxide particles B1, B2, and a step (VI) of calcining and activating the inorganic oxide particles B1, B2 supporting the chromium compound D obtained in the step (V) at 400° C. to 900° C. in a non-reducing atmosphere to convert at least a portion of the chromium atoms to a hexavalent form.
Step (V) is the same as step (I) already described, and step (VI) is the same as step (II) already described, so duplicated descriptions will be omitted.

The chromium catalyst A3 may be produced by mixing inorganic oxide particles B1 and B2 in advance, granulating the mixture to form inorganic oxide particles B3, supporting the chromium compound D on the inorganic oxide particles B3, and activating the mixture by calcination at 400° C. to 900° C. in a non-reducing atmosphere to convert at least some of the chromium atoms to hexavalent form. In this case, the chromium catalyst A3 produced has the chromium compound C1 supported on the inorganic oxide particles B1 and the chromium compound C1 supported on the inorganic oxide particles B2, and ultimately this chromium catalyst A3 is composed of combined particles in which the contact portions of the particles of the chromium catalyst A1 and the particles of the chromium catalyst A2 are bonded to each other.
The chromium catalyst A3 may be in a form in which the chromium compound C1 is supported on inorganic oxide particles B3 obtained by granulating inorganic oxide particles B1 and inorganic oxide particles B2. In this case, in the produced chromium catalyst A3, the chromium compound C1 is supported on the inorganic oxide particles B1 and the chromium compound C1 is supported on the inorganic oxide particles B2, and ultimately, this chromium catalyst A3 is composed of combined particles in which particles of the chromium catalyst A1 and particles of the chromium catalyst A2 are combined.
This ethylene-based polymerization catalyst (chromium catalyst A3) can be produced by a production method in which inorganic oxide particles B1 including plate-like particles and aggregates thereof, and amorphous inorganic oxide particles B2 are granulated to form inorganic oxide particles B3, and a chromium compound C1 is supported on the inorganic oxide particles B3.
The method for granulating to obtain the inorganic oxide particles B3 can be a known granulation method, for example, stirring granulation method, spray granulation method, rolling granulation method, and fluidized bed granulation method. Among these, spray granulation method is preferred from the viewpoint of easily maintaining the properties of the particles before mixing.
When spray granulation is performed, the dispersion medium for the raw material slurry may be an organic solvent such as water, methanol, ethanol, chloroform, methylene chloride, pentane, hexane, heptane, toluene, or xylene, with water being preferred.
During granulation, known binders such as organic substances, inorganic solvents, and inorganic salts may be used.
In the case of spray granulation, the concentration of inorganic oxide particles (total of B1 and B2) in the raw material slurry is 0.1 to 70% by weight, preferably 1 to 50% by weight. The inlet temperature of the hot air for spray granulation varies depending on the dispersion medium, but for example, water is 80 to 260° C., preferably 100 to 220° C. The mixing ratio of the plate-like inorganic oxide particles B1 and the amorphous inorganic oxide particles B2 is preferably 1:99 to 99:1, more preferably 5:95 to 95:5, and even more preferably 10:90 to 90:10, by weight.
The surface area of the chromium catalyst A3 is not particularly limited, but is usually from 10 m ² /g to 1000 m ² /g, preferably from 20 m ² /g to 950 m ² /g, and more preferably from 50 m ² /g to 900 m ² /g.
The pore volume of the chromium catalyst A3 is not particularly limited, but is usually from 0.05 to 5.0 mL/g, preferably from 0.1 to 3.0 mL/g, and more preferably from 0.1 to 2.5 mL/g.
The average particle size of the particles of the chromium catalyst A3 is not particularly limited. From the viewpoint of handling, however, the average particle size is preferably 0.1 μm or more and 200 μm or less, more preferably 0.2 μm or more and 150 μm or less, and even more preferably 0.5 μm or more and 100 μm or less.

5. Characteristics of the Ethylene-Based Polymerization Catalyst (1) Ethylene-Based Polymerization Catalyst In the present invention, in producing an ethylene-based polymer, the chromium catalyst A1 may be used alone as the ethylene-based polymerization catalyst, or the chromium catalyst A3 (chromium catalysts A1 and A2) may be used. When the chromium catalyst A1 and the chromium catalyst A2 are used in combination, any of the following methods (a) to (d) may be used.
(a) A method in which two types of catalysts are mixed and then activated in an activation furnace, and the mixed catalyst thus extracted is introduced into a polymerization reactor in the presence or absence of a solvent or in the presence or absence of an organometallic compound.
(b) A method in which two types of catalysts are activated separately in an activation furnace, and the extracted catalysts are mixed in advance in the presence or absence of a solvent or in the presence or absence of an organometallic compound, and then introduced into a polymerization reactor.
(c) A method in which two types of catalysts are activated separately in an activation furnace, and each of the extracted catalysts is introduced separately into a polymerization reactor in advance in the presence or absence of a solvent or in the presence or absence of an organometallic compound, and then mixed in one polymerization reactor.
(d) A method in which inorganic oxide particles B1 and inorganic oxide particles B2 are mixed in advance, then granulated to form inorganic oxide particles B3 (mixed support), a chromium compound (chromium compound D or chromium compound E) is supported on the mixture, and activation is performed in an activation furnace, and the extracted mixed catalyst is introduced into a polymerization reactor in the presence or absence of a solvent or in the presence or absence of an organometallic compound.

(2) Mixing ratio of chromium catalysts A1 and A2 in an ethylene-based polymerization catalyst containing chromium catalyst A3 (chromium catalysts A1 and A2) When an ethylene-based polymerization catalyst contains chromium catalyst A3, i.e., chromium catalyst A1 and chromium catalyst A2, the mixing ratio of chromium catalyst A1 to chromium catalyst A2 is not particularly limited. The mixing ratio of chromium catalyst A1 to chromium catalyst A2 is preferably 1:99 to 99:1, more preferably 5:95 to 95:5, and even more preferably 10:90 to 90:10 by weight.

(3) Content of chromium atoms in ethylene-based polymerization catalyst The content of chromium atoms in the ethylene-based polymerization catalyst is not particularly limited. From the viewpoint of preventing aggregation of the supported chromium atoms with each other and efficient activation, the content of chromium atoms is preferably 0.01% by weight to 2.0% by weight, more preferably 0.1% by weight to 2.0% by weight, and further preferably 0.2% by weight to 1.5% by weight.

(4) Components other than chromium catalysts A1 and A2 in the ethylene-based polymerization catalyst The ethylene-based polymerization catalyst may contain components other than chromium catalysts A1 and A2, so long as they do not impair the effects of the present invention.
The other components are not particularly limited, and the content (wt%) of the other components is preferably 5 wt% or less.

6. Method for Producing Ethylene-Based Polymer In the method for producing an ethylene-based polymer of the present invention, a monomer containing at least ethylene is polymerized using the above-mentioned ethylene-based polymerization catalyst.

(1) Polymerization Method The process for producing an ethylene polymer of the present invention can be carried out by a liquid phase polymerization method such as slurry polymerization or solution polymerization, or a gas phase polymerization method.
The liquid phase polymerization method is usually carried out in a hydrocarbon solvent, such as propane, n-butane, isobutane, n-pentane, isopentane, hexane, heptane, octane, decane, cyclohexane, benzene, toluene, xylene, or a mixture of such inert hydrocarbons.
In the gas phase polymerization method, a commonly known polymerization method such as a fluidized bed or a stirred bed can be used in the presence of an inert gas. In the gas phase polymerization method, a so-called condensing mode can be used in which a medium for removing polymerization heat is optionally used.
As a polymerization method, not only single-stage polymerization in which an ethylene polymer is produced using one reactor, but also multi-stage polymerization can be carried out by connecting at least two reactors. In the case of multi-stage polymerization, two reactors are connected, and a reaction mixture obtained by polymerization in a first-stage reactor is then continuously fed to a second-stage reactor, which is preferred. The transfer from the first-stage reactor to the second-stage reactor is carried out through a connecting pipe. This transfer is preferably carried out by utilizing a pressure difference caused by continuous discharge of the polymerization reaction mixture from the second-stage reactor.

(2) Polymerization Conditions The polymerization temperature in the liquid phase or gas phase polymerization method is generally 0°C to 300°C, practically 20°C to 200°C, preferably 50°C to 180°C, and more preferably 70°C to 150°C.
The catalyst concentration and ethylene concentration in the reactor can be any concentration sufficient to drive the polymerization. For example, the catalyst concentration can range from about 0.0001% by weight to about 5% by weight, based on the weight of the reactor contents, for liquid phase polymerization. Similarly, the ethylene concentration can range from 0.1 MPa to 10 MPa total pressure for gas phase polymerization.
If necessary, hydrogen can be introduced into the polymerization reactor to adjust the molecular weight.

(3) Copolymerization In the process for producing an ethylene-based polymer of the present invention, in addition to ethylene homopolymerization, α-olefins such as propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene, etc. may be introduced into a polymerization reactor alone or in combination to be copolymerized, if necessary.
The α-olefin content in the resulting ethylene copolymer is desirably 15 mol % or less, preferably 10 mol % or less.

(4) Organometallic Compound During the polymerization, an organometallic compound may be introduced as a co-catalyst and brought into contact with the ethylene-based polymerization catalyst for the purpose of finely adjusting the molecular weight or molecular weight distribution of the ethylene-based polymer or for the purpose of removing impurities in the polymerization system as a scavenger.
In particular, organometallic compounds have the effect of improving the catalytic activity of ethylene-based polymerization catalysts and the effect of making hydrogen more effective as a molecular weight regulator.
As the organometallic compound, organometallic compounds of Groups 1, 2, and 13 of the periodic table, specifically organolithium compounds, organomagnesium compounds, organoaluminum compounds, and organoboron compounds are preferably used, with organoaluminum compounds and organoboron compounds being more preferred.

The organolithium compound includes alkyllithium, specifically, methyllithium, n-butyllithium, and the like.
The organic magnesium compound includes dialkyl magnesium, specifically, butylethyl magnesium, and dibutyl magnesium.
The organoaluminum compound includes trialkylaluminum and dialkylaluminum alkoxides, specifically, trimethylaluminum, triethylaluminum, triisobutylaluminum, and diethylaluminum ethoxide.
The organoboron compound includes trialkylboranes, specifically triethylborane.
The amount of the organometallic compound to be contacted is such that the molar ratio of metal atoms to chromium atoms is 0.2 to 1,000, preferably 0.5 to 100.

The resulting ethylene-based polymer is then preferably kneaded. Kneading can be carried out using a single-screw or twin-screw extruder or a continuous kneader. The resulting ethylene-based polymer can then be molded, such as by blow molding, by a conventional method.

7. Effects of the Present Embodiment According to the ethylene-based polymerization catalyst component, the method for producing an ethylene-based polymer catalyst, and the method for producing an ethylene-based polymer of the present embodiment, it becomes possible to design an HDPE material (high density polyethylene material) having an excellent balance between durability and fluidity.

The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples as long as they do not deviate from the gist of the invention.

1. Methods for Measuring Physical Properties The methods for measuring physical properties used in the examples and comparative examples are as follows.
(1) Measurement of peak intensity in infrared spectrum of inorganic oxide particles B1 (infrared spectroscopy)
The inorganic oxide was filled into a sample holder for diffuse reflection IR in a glove box purged with high-purity argon, and the sample surface was smoothed.Then, the sample was sealed with a lid with a window and placed in an IR measurement device for measurement.
The measurement conditions are as follows.
Apparatus: FT/IR-6600 manufactured by JASCO Corporation
Detector: TGS
Photometry method: Diffuse reflection method Wavelength range: 1000 to 4000 cm ^-1
Resolution: 4 ^cm
Number of measurements: 512 Atmosphere: Argon (2) Powder X-ray Diffraction (XRD): Powder X-ray diffraction was measured using the following apparatus and conditions.
Equipment: Rigaku X-ray Diffractometer Smartlab
X-ray source: Cu-Kα rays (using Kβ absorption plate), tube voltage 40kV, tube current 30mA
Optical system: focusing method, divergence slit 2/3 degrees, scattering slit 2/3 degrees, receiving slit 0.300 mm
Scan mode: 2θ/θ scan 2θ scan range: 3.0000-55.0000 degrees Angle step width: 0.0200 degrees Scan speed: 4.0000 degrees/min Detector: scintillation counter (3) Surface area and pore volume After each silica sample was heated and thoroughly dried under reduced pressure, a nitrogen adsorption isotherm was measured at liquid temperature using a Quantachrome Autosorb 3B. The pore volume was calculated from the amount of adsorption at a relative pressure of 0.95 of the obtained adsorption isotherm, and the specific surface area was calculated by performing a BET multipoint analysis. Furthermore, the average pore diameter was calculated according to formula (1) by assuming the pore structure to be cylindrical. In this formula, D _ave indicates the average pore diameter, V _total indicates the pore volume, and S _BET indicates the specific surface area by the BET multipoint method.
D _ave =4V _total /S _BET formula (1)
Furthermore, the mesopore distribution was determined by BJH analysis, and the pore volume in a specified range was calculated.
(4) SEM Observation: SEM observation was carried out using the following equipment and conditions.
Equipment: Hitachi FE-SEM
Pressurizing voltage: 1 kV
Equipment magnification: 20k
WD: 4mm
(5) HLMI: Measured in accordance with ASTM-D-1238-57T at 190° C. and a load of 21.6 kg.
(6) Hexavalent chromium content: An aqueous NaOH solution (0.1 M) was added to the catalyst component to dissolve hexavalent chromium, and a portion of the solution was sampled and the absorbance at a wavelength of 366 nm was measured to determine the content.
(7) Average particle size: Measurement was performed using a laser diffraction/scattering type particle size distribution measuring device LA-920 manufactured by Horiba, Ltd. under the conditions of a dispersion solvent of ethanol, a refractive index of 1.0, and a shape factor of 1.0, and the median diameter was taken as the average particle size.

2. Examples and Comparative Examples (1) Example 1
(1.1) Infrared spectrum of inorganic oxide particles B1 The infrared spectrum of "Sun Lovely" (manufactured by AGC Si-Tech Co., Ltd.), which is inorganic oxide particles B1, is shown by a solid line in Figure 1. As shown in Table 1, in this infrared spectrum, the maximum peak in range X was 3661 cm ^-1 , and the peak intensity Px was 1.32. Furthermore, the maximum peak in range Y was 3746 cm ^-1 , and the peak intensity Py was 0.88. The peak intensity ratio Py/Px was 0.67.
(1.2) Structural Analysis Data of Inorganic Oxide Particles B1 Structural analysis data of inorganic oxide particles B1 are as follows.
<Structural Analysis Data of Inorganic Oxide Particles B1>
XRD: Peak at 2θ=25.8°, half width 1.5°
BET method: Surface area 84m ² /g
Pore volume: 0.2 mL / g
_SiO2 purity: 99.5% (weight basis)
(1.3) Preparation of chromium catalyst A1 Inorganic oxide particles B1 were impregnated with an aqueous solution of chromium acetate, and then water was removed to obtain chromium-containing silica with a chromium content of 0.5% by weight. The chromium-containing silica was then activated under dry air atmosphere at 600°C for 20 hours to obtain chromium catalyst A1 (Phillips type catalyst). Upon activation, the chromium-containing silica changed color from light blue to light orange. This indicates that the chromium atoms were converted to hexavalent chromium. Substantially 99% by weight of trivalent chromium was converted to hexavalent chromium.

(1.4) Physical properties of chromium catalyst A1 The peak position of the XRD of chromium catalyst A1 hardly changed between inorganic oxide particles B1 (raw material) dried at 200°C and chromium catalyst A1 supported with chromium acetate and activated at 600°C. This means that inorganic oxide particles B1 have good thermal stability. An SEM image of chromium catalyst A1 is shown in Figure 3.

(1.5) Ethylene Polymerization Into a 1.5 L polymerization vessel thoroughly purged with nitrogen, 185 mg of chromium catalyst A1 and 700 mL of isobutane were placed, and the internal temperature was raised to 100°C.
Then, ethylene was injected, and polymerization was carried out for 120 minutes at a polymerization temperature of 100° C. while maintaining the ethylene partial pressure at 1.4 MPa. Then, the polymerization was terminated by discharging the content gas to the outside of the system. As a result, 21 g of an ethylene-based polymer was obtained. The HLMI of the obtained ethylene-based polymer was that the polymer did not flow. Therefore, it was judged to be less than 0.01 g/10 min. The density was 0.9520 g/cm ³ .

(2) Example 2
(2.1.1) Preparation of chromium catalyst A1 Prepared in the same manner as in Example 1.
(2.1.2) Preparation of chromium catalyst A2 Inorganic oxide particles B2 (amorphous silica aggregates) were impregnated with an aqueous solution of chromium acetate, and then water was distilled off to obtain chromium-containing silica with a chromium content of 1.0% by weight. The chromium-containing silica was then activated under dry air atmosphere at 820°C for 18 hours to obtain chromium catalyst A2 (Phillips type catalyst). Upon activation, the chromium-containing silica changed color from light blue to light orange. This indicates that the chromium atoms were converted to hexavalent chromium. Substantially 99% by weight of trivalent chromium was converted to hexavalent chromium.
The infrared spectrum of inorganic oxide particles B2 is as described later in the section "(3.1) Infrared spectrum of inorganic oxide particles B2". The structural analysis data of inorganic oxide particles B2 is as described later in the section "(3.2) Structural analysis data of inorganic oxide particles B2".

(2.2) Ethylene Polymerization Into a 1.5 L polymerization vessel thoroughly purged with nitrogen, 152 mg of chromium catalyst A1, 39 mg of chromium catalyst A2 and 700 mL of isobutane were placed, and the internal temperature was raised to 100°C.
Then, ethylene was injected, and polymerization was carried out for 120 minutes at a polymerization temperature of 100° C. while maintaining the ethylene partial pressure at 1.4 MPa. Then, the content gas was discharged to the outside of the system to terminate the polymerization. As a result, 200 g of an ethylene-based polymer was obtained. The HLMI of the obtained ethylene-based polymer was 5.1 g/10 min, and the density was 0.9577 g/cm ³ .

(3) Comparative Example 1
(3.1) Infrared spectrum of inorganic oxide particles B2 The infrared spectrum of inorganic oxide particles B2 is shown by a dashed line in Figure 1. As shown in Table 1, in this infrared spectrum, the maximum peak in range X was 3697 cm ^-1 , and the peak intensity Px was 0.42. The maximum peak in range Y was 3747 cm ^-1 , and the peak intensity Py was 5.82. The peak intensity ratio Py/Px was 13.86.
(3.2) Structural Analysis Data of Inorganic Oxide Particles B2 The structural analysis data of inorganic oxide particles B2 is as follows.
<Structural Analysis Data of Inorganic Oxide Particle 2>
XRD: A broad peak characteristic of amorphous material at around 2θ=22° BET method: Surface area: 310 m ² /g
Pore volume: 1.7 mL / g
_SiO2 purity: 99.8% (weight basis)
(3.3) Preparation of chromium catalyst A2 It was prepared in the same manner as in Example 2.

(3.4) Ethylene Polymerization Into a 1.5 L polymerization vessel thoroughly purged with nitrogen, 29 mg of chromium catalyst A2 and 700 mL of isobutane were placed, and the internal temperature was raised to 100°C.
Then, ethylene was injected, and polymerization was carried out for 120 minutes at a polymerization temperature of 100° C. while maintaining the ethylene partial pressure at 1.4 MPa. Then, the content gas was discharged to the outside of the system to terminate the polymerization. As a result, 149 g of an ethylene-based polymer was obtained. The HLMI of the obtained ethylene-based polymer was 9.8 g/10 min, and the density was 0.9582 g/cm ³ .

(4) Example 3
(4.1) Preparation of chromium catalyst A3 Inorganic oxide particles B2-2 (amorphous silica aggregates, 40 g, average particle size 12 μm) and inorganic oxide particles B1 (120 g, average particle size 4.3 μm) used in Example 1 were slurried in 340 mL of distilled water. This slurry was spray-dried and granulated using a spray-drying granulation device (Okawahara Kakoki Co., Ltd. "L-8") under the following conditions:
Atomizer type: M type rotary disc Atomizer rotation speed: 10,000 rpm
Slurry supply rate: 1.0 L / h
Inlet temperature: 150°C
As a result of the granulation, inorganic oxide particles B3 having an average particle size of 37.5 μm were collected from the bottom of the main body.
The inorganic oxide particles B3 obtained were impregnated with an aqueous solution of chromium acetate, and then the water was removed to obtain chromium-containing silica with a chromium content of 0.5% by weight. The chromium-containing silica was then activated under dry air atmosphere at 730°C for 12 hours to obtain chromium catalyst A3 (Phillips type catalyst). The activation caused the chromium-containing silica to change color from light blue to light orange. This indicates that the chromium atoms were converted to hexavalent chromium. Substantially 99% by weight of trivalent chromium was converted to hexavalent chromium.
<Structural Analysis Data of Inorganic Oxide Particle B2-2>
XRD: A broad peak characteristic of amorphous material at around 2θ=22° BET method: Surface area: 320 m ² /g
Pore volume: 1.6 mL / g
_SiO2 purity: 99.8% (weight basis)
Average particle size: 12 μm
(4.2) Ethylene Polymerization Into a 2.0 L polymerization vessel thoroughly purged with nitrogen, 130 mg of the chromium catalyst A3 obtained in Example 3 (4.1) and 800 mL of isobutane were placed, and the internal temperature was raised to 100°C.
Then, ethylene was injected, and polymerization was carried out for 200 minutes at a polymerization temperature of 100° C. while maintaining the ethylene partial pressure at 1.4 MPa. Then, the content gas was discharged to the outside of the system to terminate the polymerization. As a result, 340 g of an ethylene-based polymer was obtained. The HLMI of the obtained ethylene-based polymer was 1.0 g/10 min, and the density was 0.9522 g/cm ³ .
(5) Comparative Example 2
(5.1) Preparation of chromium catalyst A4 The inorganic oxide particles B2-2 (amorphous silica aggregates, 100 g, average particle size 12 μm) of Example 3 were slurried in 400 mL of distilled water. This slurry was treated in the same manner as in Example 3 (4.1) using a spray drying granulation device (Okawahara Kakoki Co., Ltd. "L-8") to obtain granules of inorganic oxide particles B2-2 having an average particle size of 98.2 μm.
The obtained inorganic oxide particle B2-2 granules were impregnated with an aqueous solution of chromium acetate, and then the water was distilled off to obtain chromium-containing silica having a chromium content of 0.5% by weight. The chromium-containing silica was then activated under conditions of 730°C and 12 hours in a dry air atmosphere to obtain chromium catalyst A4 (Phillips type catalyst). Upon activation, the chromium-containing silica changed color from light blue to light orange. This indicates that the chromium atoms were converted to hexavalent chromium. Substantially 99% by weight of trivalent chromium was converted to hexavalent chromium.
(5.2) Ethylene Polymerization Into a 2.0 L polymerization vessel thoroughly purged with nitrogen, 60 mg of the chromium catalyst A4 obtained in Comparative Example 2 (5.1) and 800 mL of isobutane were placed, and the internal temperature was raised to 100°C.
Then, ethylene was injected, and polymerization was carried out for 60 minutes at a polymerization temperature of 100° C. while maintaining the ethylene partial pressure at 1.4 MPa. Then, the content gas was discharged to the outside of the system to terminate the polymerization. As a result, 170 g of an ethylene-based polymer was obtained. The HLMI of the obtained ethylene-based polymer was 2.5 g/10 min, and the density was 0.9562 g/cm ³ .

3. Consideration of the results of the Examples and Comparative Examples The results of the Examples and Comparative Examples are shown in Tables 1 and 2. Note that the polymer density in Table 2 is a value rounded off to the third decimal place.

As shown in Table 2, a comparison between Example 1 and Comparative Example 1 shows that an ethylene-based polymer having a high molecular weight can be obtained by using chromium catalyst A1, which is a carrier made of an inorganic oxide having a Px/Py ratio of less than 10. A comparison between Example 2 and Comparative Example 1 shows that a mixture of chromium catalyst A1 and chromium catalyst A2 can be used to obtain an ethylene-based polymer having a higher molecular weight than an ethylene-based polymer obtained from chromium catalyst A2 alone. In addition, Example 2 has a lower HLMI (higher PE molecular weight) than Comparative Example 1, but the density is the same. This is a preferable balance of physical properties for materials for blowing. Furthermore, a comparison between Example 3 and Comparative Example 2 shows that a ethylene-based polymer having a higher molecular weight can be obtained from chromium catalyst A3, which uses a carrier made by mixing and granulating inorganic oxide particles B1, which are plate-like silica aggregates, and inorganic oxide particles B2-2, which are amorphous silica aggregates, than from a carrier made by granulating inorganic oxide particles B2-2, which are amorphous silica aggregates, alone.
From the above results, it was confirmed that _an ethylene-based polymer having an ultrahigh molecular weight component can be produced by using an ethylene-based polymerization catalyst containing plate-like silica aggregates (planar silica aggregates) having a peak intensity ratio Py/Px of less than 10 and containing 90% by weight or more of SiO2.

The present invention is not limited to the embodiments detailed above, and various modifications and variations are possible within the scope of the claims of the present invention.

According to the present invention, an ethylene-based polymer having an ultra-high molecular weight component can be produced. This ethylene-based polymer can be used in a wide range of applications, and is therefore highly valuable industrially.

Claims (6)

The sample was calcined at 600° C. for 24 hours as a pretreatment for analysis, and then measured. The sample contained a plate-like inorganic oxide having the following properties 1 and 2:
The ethylene polymerization catalyst component , wherein the inorganic oxide is Sunlovely (a product name of AGC Si-Tech Co., Ltd.) .
Property 1: In an infrared spectrum, the ratio Py/Px of a peak intensity Py having a maximum in a range Y of 3700 cm ^-1 to 3799 cm ^{-1 to a peak intensity Px having a maximum in a range X of 3600 cm -1 to} 3699 cm ^-1 is less than 10.
Property 2: Contains 90% or more by weight of _SiO2 . The ethylene-based polymerization catalyst component according to claim 1, characterized in that the inorganic oxide has a peak in powder X-ray diffraction at 2θ = 23° to 29° with a half-width of 0.2° to 5°, indicating crystallinity. A step (I) of supporting a chromium compound on the ethylene-based polymerization catalyst component according to claim 1 or 2;
A step (II) of calcining and activating the chromium compound-supported component obtained in the step (I) at 400° C. to 900° C. in a non-reducing atmosphere to convert at least a part of chromium atoms into hexavalent chromium atoms;
2. A method for producing an ethylene polymerization catalyst comprising the steps of: The method for producing an ethylene polymerization catalyst according to claim 3, characterized in that in step (I), the chromium compound-supported component containing 0.01% by weight to 2.0% by weight of chromium atoms is obtained. The method for producing an ethylene-based polymerization catalyst according to claim 3 or 4, characterized in that in step (II), 50% or more of the chromium atoms contained in the chromium compound-supported component are oxidized to hexavalent chromium. A method for producing an ethylene-based polymer, comprising polymerizing a monomer containing at least ethylene using an ethylene-based polymerization catalyst obtained by the production method according to any one of claims 3 to 5.

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